This invention relates generally to thrust bearings and, more particularly, to thrust bearings used with springs to provide preload and thrust bearings with enhanced flow of lubricant.
Many thrust bearing applications, for example, air conditioning compressors, rely upon thrust bearings to provide preload for rotors and shafts to maintain design clearances. Lubrication of such bearings may be provided by a refrigerant/lubricant mixture, which generally has inferior lubrication properties than pure lubricants. In most cases, the components of such thrust bearing are installed separately, directly into the compressor. In addition to being a tedious and expensive operation, this separate installation procedure introduces risks of contamination, component misalignment, and even omission of some thrust bearing components.
FIGS. 1 and 2 illustrate a thrust bearing configuration according to current practice, before and after application of an axial load, respectively. Such loads are applied during assembly of an air compressor to stabilize the axial position of the compressor shaft. In general, the environment of the thrust bearing consists of a housing 10 in which a stepped diameter or a snap ring 13 in a groove is situated to act as a support for the thrust bearing components. A spring washer 16 is positioned adjacent one of two thrust races 14 that are separated by rolling elements 15 that are guided by a bearing cage 11.
An air conditioning compressor shaft 20 has a shoulder 12 against which one thrust race 14 rests, such that when a sufficient axial preload is applied to the compressor shaft, the spring washer 16 is compressed as illustrated in FIG. 2. As can be seen in the Figure, the bearing cage 11 and the thrust races 14 are piloted on the compressor shaft 20 so that there is radial clearance 17 between the thrust races 14 and the housing 10 but little radial clearance 18 between the thrust races 14 and the shaft 20. The arrows in FIG. 2 indicate that the supply of refrigerant/lubricant mixture supplied to the clearance 18 is adequate, but the amount that reaches the clearance 17 is substantially reduced. This reduced refrigerant/lubricant supply may not provide the required amount of lubrication for protection of the thrust bearing from wear, overheating, and build-up of contaminant.
In addition to problems of inadequate flow of refrigerant/lubricant, thrust bearing performance in such applications may be degraded due to cross piloting of the thrust races 14 between the compressor shaft 20 and the housing 10. This is apparent in FIG. 2, in which the retaining snap ring 13, the spring washer 16, and the thrust race 14 are in face-to-face contact. The thrust race that is piloted on the compressor shaft 20 is intended to rotate with the shaft, and the washer 16 and snap ring 13 are restrained by the housing 10. The rotation of the thrust race 14 is frictionally resisted by the spring washer 16, rotation of which, in turn, is frictionally resisted by the snap ring 13. This piloting arrangement leads to increased wear between the components. In the worst case, the retaining snap ring 13 may be driven by the spring washer 16 to turn in the housing and eventually slip out of the groove in which it is installed due to wear. When combined with the inadequate lube flow already described, the build-up of wear contaminant in the thrust bearing progresses at an increasing rate and may lead to premature thrust bearing failure.
The foregoing illustrates limitations known to exist in present thrust bearing configurations. Thus, it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
In one aspect of the present invention, this is accomplished by providing a thrust bearing assembly comprising two thrust races, a plurality of rolling elements between and against the two thrust races, for facilitating relative rotation of the thrust races about a common axis, and a spring washer. The spring washer is axially outward of the two thrust races for engaging a support surface and for applying a preload to a first of the two thrust races. Retention means retains the two thrust races, the rolling elements and the spring washer together as an assembly to facilitate handling and installation.
The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.